Ethylene oxide (EtO) is a commonly used, highly effective, sterilizing gas. Although ethylene oxide is vitally important to health care providers, to manufacturers and sterilizers of medical products and to spice and other food manufacturers, all of which use ethylene oxide as a sterilant, ethylene oxide has been determined to be toxic. Various federal agencies, including the Environmental Protection Agency and the National Institute for Occupational Safety and Health, have recently recommended standards and exposure levels to reduce permissible exposure limits for a worker exposed to or working with ethylene oxide from fifty parts of ethylene oxide per million parts of air during an eight hour period to one part per million parts of air during an eight hour period.
Prior art sensors for the measurement of ethylene oxide and other noxious gases are known, such as photoionization sensors, gas chromatographic sensors and infrared sensors, and are commonly in the form of infrared sensors. See, e.g., Monitoring Ethylene Oxide With Direct Reading Instrumentation by Charles W. Opp, Chapter 7, "The Safe Use of Ethylene Oxide, Proceedings of An Educational Seminar," HEMA Report 80-4, December 1980. However, these prior art ethylene oxide and other noxious gas sensors suffer from a variety of problems, including unacceptable specificity, inability to accurately measure low airborne concentrations, reproducability of measurements, inappropriately long response times, portability problems, short measurement life and high cost.
Electrochemical gas sensors and devices are also well known in the prior art. See, e.g., U.S. Pat. Nos. 4,184,937; 3,992,267; 3,824,167; and 3,776,832. These sensors and devices are used to detect a variety of noxious gases, including hydrogen sulfide, chlorine, nitric oxide, carbon monoxide and various hydrocarbons. However, it is presently believed that no one has successfully developed to date an electrochemical cell for the accurate detection and measurement of ethylene oxide and other noxious gases at levels as low as one part per million and less.
A need, therefore, exists for an electrochemical cell for the continuous measurement of noxious gases, such as ethylene oxide, ethylene glycol, ethanol, acetaldehyde, acetone, isoproponal, propylene oxide and other two to four carbon chain gases, having good selectivity, good sensitivity, the ability to measure airborne levels at one part per million and less, good reproducability, a good measurement life and a reasonable cost.